The degree of integration of integrated circuits has recently become much higher, and the processing of superfine patterns having a line width of a half micron or below is required in the production of semiconductor substrate for VSLI. In order to meet such a requirement, a wavelength of light source used in an exposure apparatus for photolithography becomes shorter, and nowadays the use of an excimer laser beam (e.g., XeCl, KrF or ArF) in a short wavelength region of a far ultraviolet ray is investigated.
As a resist for use in the pattern formation by the photolithography in such a wavelength region, a chemically amplified resist is known.
A chemically amplified positive resist composition is a pattern formation material in which an acid is generated in the exposed area upon irradiation of radiation, for example, a far ultraviolet ray, and solubility in a developer between the exposed area and unexposed area is differentiated by a reaction using the acid as a catalyst, whereby a pattern is formed on a substrate.
In general, the chemically amplified resist is roughly divided into three types, the so-called two-component, two point five-component and three-component types. The chemically amplified resist of two-component type comprises a combination of a compound (hereinafter referred to as a “photo-acid generator” sometimes) capable of generating an acid by photolysis with a binder resin. The binder resin combined with the photo-acid generator is a resin having in its molecule, a group (hereinafter referred to as an “acid-decomposable group” sometimes) capable of being decomposed by the action of an acid to increase the solubility of resin in an alkali developing solution. The resist of two point five-component type further contains a low molecular weight compound having an acid-decomposable group in addition to the above described two components. The resist of three-component type contains a photo-acid generator, an alkali-soluble resin and the low molecular weight compound described above.
Although the chemically amplified resist described above is a photoresist suitable for exposure to an ultraviolet ray or a far ultraviolet ray, it is still necessary for the resist to meet requirements for characteristics from the standpoint of practical use.
Since the composition is mainly composed of a resin having as a basic skeleton, poly(hydroxystyrene) that has a small absorption in a region of 248 nm, a good pattern with high sensitivity and high resolution is formed, when a KrF excimer laser is used as a light source for exposure. Thus, the composition is superior to a conventional resist composition using a naphthoquinonediazide/novolac resin.
When a light source having a shorter wavelength, e.g., an ArF excimer laser (193 nm) is used for exposure, on the other hand, since an aromatic group-containing compound essentially has a large absorption in a region of 193 nm, the above-described chemically amplified composition is still insufficient.
The use of poly(meth)acrylate as a polymer having a small absorption in a wavelength range of 193 nm is described in J. Vac. Sci. Technol., B9, 3357(1991). The polymer has, however, a problem in that resistance to dry etching ordinarily performed in a semiconductor production process is low in comparison with conventional phenolic resins having an aromatic group.
Further, as a photoresist composition for an ArF light source, a resin into which an alicyclic hydrocarbon moiety is proposed for the purpose of improving dry etching resistance. However, the introduction of alicyclic hydrocarbon moiety is accompanied with a problem in that a system including the resin becomes extremely hydrophobic, and it is difficult to perform development with an aqueous solution of tetramethylammonium hydroxide (hereinafter referred to as TMAH sometimes), which has hitherto been widely employed as a developer for resist. Also, a phenomenon of releasing the resist film from a substrate during the development is observed.
In response to the increase in the hydrophobic property of resist, an attempt has been made that an organic solvent, for example, isopropyl alcohol is added to the developer. Although the good result is recognized to a certain extent, other problems, for example, fear of swelling the resist film and complexity of the process arise. Thus, the problem is not always solved. As to an approach to improvement in the resist, many attempts of compensation for the various hydrophobic alicyclic hydrocarbon moieties by the introduction of hydrophilic groups have been made.
An energy-susceptive resist material containing a polymer obtained by polymerization of a monomer having an alicyclic structure, for example, a norbornene ring in the main chain, maleic anhydride and a monomer having a carboxylic acid is described in JP-A-10-10739 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). A radiation-sensitive resin composition containing a resin having an alicyclic skeleton in the main chain and a radiation-sensitive acid generator is described in JP-A-10-111569. A radiation-sensitive material comprising a resin having an alicyclic functional group containing a polar group and an acid-decomposable group is described in JP-A-11-109632.
A photoresist composition containing a copolymer obtained by polymerization of a (meth)acrylate derivative having a lactone structure with another polymerizable compound is described in Japanese Patent 3,042,618.
As described above, a resin having an acid-decomposable group, which is used in a photoresist for exposure to a far ultraviolet ray, ordinarily has also an aliphatic cyclic hydrocarbon group in the molecule. As a result, the resin becomes hydrophobic and the problems resulting from the hydrophilicity occur. Although the various methods described above have been investigated in order to solve these problems, the results obtained by these methods are still insufficient and further improvement is desired.
Also, a triarylsulfonium salt acid generator and a phenacylsulfonium salt acid generator are known as acid generators for chemically amplified positive resist composition. However, these acid generators are low in sensitivity, since the triarylsulfonium salt acid generator has a large absorption at a wavelength of 193 nm and the phenacylsulfonium salt acid generator is inferior in the acid-generating property.
Further, an acid generator mixture of a specific sulfonium salt (an anion having from 1 to 15 carbon atoms) and a triarylsulfonium salt is described in JP-A-2000-292917, a combination of a triphenylsulfonium salt of a perfluoroalkanesulfonic acid having from 4 to 8 carbon atoms and a 2-alkyl-2-adamantyl(meth)acrylate is described in JP-A-2000-275845, and an acid generator mixture of a specific sulfonium salt (an anion having from 1 to 8 carbon atoms) and a triphenylsulfonium salt or iodonium salt of a perfluoroalkanesulfonic acid having from 4 to 8 carbon atoms is described in EP 11041,442A.
It is the common practice to use modified illumination or a phase shift mask in order to satisfy a further miniaturization tendency of patterns. Annular illumination has been used for the formation of line and space patterns, while a halftone phase shift mask has been used for the formation of contact holes.
When the annular illumination is used, high resolution and a broad defocus latitude are requested. The term “broad defocus latitude” means that fluctuation in line width due to defocus is small.
When the halftone phase shift mask is used, the pattern portions are dissolved by slight transmitted light, thereby causing a problem of sidelobe. It is also desired to solve the problem of sidelobe.
According to the request on the miniaturization of semiconductor chips in recent years, patterns of semiconductor reach to a fine range of from 0.13 to 0.35 μm. However, conventional resist compositions have a problem in that the resolution of pattern is poor owing to factors, for example, edge roughness of line pattern. The term “line edge roughness” used herein means unevenness of edge which results from irregular fluctuation of an edge of top portion and an edge of bottom portion in the direction vertical to the line due to the characteristics of resist, when the pattern is observed from just above.
Moreover, there are other problems of hole pitch dependency, exposure margin and fluctuation of sensitivity during preservation with the lapse of time. Also, a problem in that PED stability with the lapse of time in or out of an exposure apparatus degrades and the pattern size is changed occurs. The term “PED stability” used herein means stability of a coated film when the coated film is allowed to stand after the exposure in or out of the exposure apparatus until conducting a heat treatment.
A positive photoresist composition containing an acid-decomposable resin having a specific lactone structure is described in JP-A-2001-109154. The positive photoresist composition has high sensitivity and high resolution and is excellent in the edge roughness of pattern. However, when it is used together with a photo-acid generator conventionally used, exposure margin and development defect are poor, and further improvement has been desired.